This invention relates to servo mechanisms and is particularly although not exclusively concerned with pneumatic servo mechanisms for use in vehicle braking systems or the like.
It is known to provide pneumatic servo mechansims in vehicle braking systems. With a view to reducing the thickness and weight of the housings of such mechanisms, there has been proposed a servo mechanism in which a tie rod extends through a housing and a piston within. Depending on the particular application, the tie rod may have the function of connecting together two portions of the housing, and also be adapted to be secured to a supporting surface at one end, and carry a device to be operated by the servo mechanism at the other end. In such an arrangement, the piston must be adapted to move with respect to the tie rod, and the problem therefore exists of providing a fluid-tight seal between the movable piston and the tie rod.
Preferred embodiments of the present invention aim to provide an arrangement which affords such fluid-tight sealing in such servo mechanisms.
More generally, according to the present invention, there is provided a servo mechanism comprising a pressure housing, a piston movably mounted in the housing, a diaphragm co-operating with the piston and housing to define within the housing two pressure chambers at opposite faces of the piston, a tie rod extending through the housing and piston, and a boot secured around the tie rod in a substantially fluid-tight manner, one end of the boot being secured to the tie rod or housing, and the other end of the boot being secured to the piston.